quicklisp does not lock system-index.txt file

[guicho271828]

When two processes run in parallel, valious asdf-related calls (e.g. system-relative-pathname in my case) simultaneously tries to delete system-index.txt.bak which fail because another process has already deleted it.
Candidate solutions:

• Take some form of file lock on system-index.txt
• Ignore the error and just ensure the backup file is deleted
• Name the backup file with a hash value to minimize the collision

[guicho271828]

I've run into this problem on a compute cluster running on IBM GPFS[1] but it would not be the cause of the problem.
[1] https://www.ibm.com/support/knowledgecenter/en/SSPT3X_3.0.0/com.ibm.swg.im.infosphere.biginsights.product.doc/doc/bi_gpfs_overview.html